Our studies during the first year of this grant have demonstrated that certain cellular components of mature cultures of avian and mammalian nervous system possess a porphyrin-heme biosynthetic pathway. This pathway is subject to inhbition by lead and by high levels of chlorinated hydrocarbons. Our further studies have suggested that the inhibition by lead can be circumvented by supplying exogenous heme to lead-exposed cultures. This latter observation appears to confirm that at least some of the toxic effects of lead in the nervous system may be mediated through the porphyrin-heme metabolic pathway(s). The research described in the application is designed to 1) further investigate the nature of the porphyrin-heme biosynthetic pathway in organotypic cultures of nervous system and 2) to study the effects, in this tissue culture model, of two environmental toxic agents, lead and chlorinated hydrocarbons. We propose to localize and characterize the porphyrin biosynthetic pathway(s) in living nervous tissues using fluorescence microscopic and spectrofluorometric methods. In mature cultures treated with lead, light and electron microscopic techniques will be applied to study cellular components which are affected by lead, i.e., neuronal elements versus supporting elements; spectrofluorometric techniques are being used to measure differences in porphyrin production of lead-treated cultures compared to non-lead-treated cultures. In immature cultures, effects of lead on normal growth and development and on porphyrin heme in preventing or reversing effects of lead will also be studied. In mature cultures treated with chlorinated hydrocarbons (polychlorinated biphenyls-PCB's), biochemical and morphological effects will be studied in relationship to nervous system porphyrin-heme pathways.